Are you sure your pulley is accurate?  the most accurate way to test is
to get a bolt that will fit the spark plug threads, remove all the plugs
and insert the bolt deep enough to interfere with the piston when it it
near the top of it's stroke.  By hand, of course, slowly turn the pulley
until the piston touches the bolt, mark the spot at the case centerline
on the  pulley, turn the engine the other way until it hits the bolt and
make another mark.  If the dead center notch in the pulley is not
exactly in the middle of the two marks, your pulley is miscalibrated.
Get a degree wheel insert from the Bus Depot and install it with your
new calibration  marks.

A mis-installed cam is more difficult.  You will need the degree wheel
mentioned above, and the cam specs.  You will have to detect with a dial
indicator or by feel that the lift is starting at a rocker arm at the
specified degree as measured on the degree wheel.  Lots of fun!
--
Stuart MacMillan
Manager, Case Program
800-909-8244 ext 208

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